[The effects of the short-term ex vivo expansion on the adhesion characteristics and chemotactic function of expanded ex vivo CD34(+) cells].

Objective: To study the effect of ex vivo expansion on the adhesion activities and chemotactic function of umbilical cord blood (UCB) hematopoietic stem and progenitor cells (HSPCs).

Methods: CD34(+) cells isolated from fresh UCB samples were cultured in serum-free and stroma-free culture system. After 7, 10 and 14 days' culture, CD34(+) cells were re-selected from the expanded products. Stromal cell- derived factor-1 (SDF-1) 100 ng/ml was added into the experimental CD34(+) cells and the absorbance at 570 nm of all groups was examined. 20 micro g/ml fibronectin (Fn) was added and the spontaneous adhesion between CD34(+) and FN was detected by MTT method. The homing-related functions including expression of homing-related adhesion molecules (CAM), adhesion activity and chemotactic function of the re-selected CD34(+) cells were evaluated and compared with those of the initial fresh CD34(+) cells.

Results: (1) The expression of CD49d, CD44, CD11a and CD49e on expanded CD34(+) cells increased or sustained the same levels as those of the fresh isolated UCB CD34(+) cells, while the expression of CD62L, CD54 and CD31 on expanded CD34(+) cells declined during the culture. (2) The spontaneous adhesion between CD34(+) and FN and SDF-1-induced adhesion continuously increased in the course of the first 10-day culture. The spontaneous adhesion rate and SDF-1-induced adhesion rate on day 0, day 7 and day 10 were 28% and 63%, 60% and 70%, 63% and 90% respectively. (3) The migration efficiency of re-selected CD34(+) cells on day 7 was almost the same compared to that of fresh CD34(+) cells.

Conclusion: The expanded HSPCs sustain most of the homing-related characteristics and activities during one-week culture while extended culture may partly impair their intrinsic homing potential.